Drilling rigs are used for drilling new wellbores, and workover units typically are for servicing or repairing completed wells. Drilling rigs usually comprise a broad range of machinery that is assembled and set up in a modular manner at a well site. Workover units, on the other hand, comprise a generally self-contained vehicle carrying various well-servicing equipment. After traveling to a well site, the workover vehicle and its equipment are often used for installing and removing tubing and sucker rods associated with the wellbore.